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tiie form assumed in rural areas." Later on, as isolation of scarlet fever was increasingly introduced
in the towns, there was unquestionably a tendency to include all cases of membranous sore throat in
the category of scarlet fever—this tendency certainly existed in London, in 1887, at which time, indeed,
cases certified to be of diphtheria were only just beginning to be admitted to hospitals of the Metropolitan
Asylums Board. Gradually, too, as years passed by, cases of laryngeal diphtheria, until then known
as "croup," were swept into the diphtheria net; so it came about that the London diphtheria deathrate,
which had already, in 1878, outstripped that for the country as a whole, maintained a distinctly
higher level for the next succeeding 10 years; then, in 1888, the London rate began to show a still more
marked rise which continued until, in 1893, it more than doubled that in England and Wales. This
invasion of the towns, as contrasted with the rural areas, has been ascribed to various causes; it was
suggested quite soon after its development that "school influence" was playing a part in promoting
it; there can surely be no doubt that in some measure it was due to the much more extended use of
methods of bacteriological diagnosis in the towns as contrasted with the country areas.
Enough has been said to show that in studying the behaviour of throat illness in recent years,
attention must be directed to scarlet fever as well as to diphtheria, and that regard must be paid to the
particular phases exhibited by the waves of epidemic prevalence of both these diseases.
Flea prevalence
in
relation lo
waves of
scarlet (ever
prevalence.
Inasmuch as major waves of throat illness culminated in 1907 and in 1914, and as the last-named
wave was declining in 1915, it was to be expected that there would be low prevalence in 1916. In point
of fact, diphtheria was only slightly prevalent, and scarlet fever was at a phenomenally low level. On
examination of the special circumstances associated with this very low prevalence of scarlet fever two
possibilities, which may themselves stand in cause and effect relationship one with the other, present
themselves. It has been suggested in previous reports that fleas arc concerned in transmitting scarlet
fever. In 1916, as in the preceding 7 years, a flea curve was constructed, and it was again found, as
in each of the previous years, that the maximum of flea prevalence shortly ante-dated that of scarlet
fever. As regards annual variations in flea prevalence, it would appear that in 1915 and 1916, the figures
showed decline after the rise which had culminated in 1914. There is, in point of fact, noteworthy
correspondence between the curves showing annual prevalence of fleas and scarlet fever during the last
8 years—the periods for which records are available. The figure for 1910 was somewhat exceptional,
but the probable reason for this was stated in the Annual Report for 1911 (p. 62). The record which has
been kept for eight years thus establishes three facts of interest with regard to flea and scarlet fever
prevalence. First, there is striking similarity of the two seasonal curves ; second, the flea maximum
always antedates the scarlet fever maximum ; third, the curves showing annual variations of fleas
and scarlet fever manifest close correspondence.
Influence of
dry seasons.
Turning now to the second possibility; the question as to the effect of dry seasons which has been
already adverted to, needs to be considered. The year 1916 was a wet year, and particularly so in SouthEast
England, and in London; this is a fact which has had a considerable influence upon mortality
returns for the year. Low diarrhoea prevalence and lessened mortality from scarlet fever and diphtheria
may undoubtedly be in part ascribed to this cause. I)r. Hugh Robert. Mill prepares each year for "British
rainfall" a map showing the percentage deviation from the average rainfall in different parts of the
British Isles. The map for 1916 shows that in South-East England the deviation from the average
was notably excessive, and the "culmination of this wet area was in a rough circle extending from London
to Maidstone, and from Enfield to Horsham, where the excess was more than 30 per cent., and about
East Grinstead, where it rose to 40 per cent. Within part of this circle the rainfall has been above the
average every year since 1908, and a spell of 8 consecutive wet years is so rare that we may confidently
expect the swing of the pendulum at an early date."
Dr. Mill adds, "In conclusion, may I be allowed to answer No, to the inevitable question ? The
data do not justify us in attributing the wetness of the past 3 years to the war. For amount of rain
1912 was much more remarkable, while as to distribution of rain in the South-East of England, where,
if anywhere, the effect of gunfire on rainfall should be clearest, the same general type of distribution
has prevailed since 1909, and the years 1910, 1912, 1915, and 1916 are remarkable for their similarity
and must, I think, owe that similarity to similar conditions in the flow of the great rain-bearing air
currents over the Atlantic." As regards the first reason, the fact that 1912 was very wet does not
materially affect the argument, and no great importance can attach to the second ground of objection
taken. As a matter of fact, Dr. Mill's maps show the special characteristics more particularly in 1915
and 1916, and though 1910 and 1912 also present some approach to similarity of type, this does not
preclude the possibility of special influence having been at work in 1915 and 1916. (1914 hardly counts
for war effects were comparatively little developed in that year.) This view of the question seems to
be held by Sir John Moore (Bri'ish Medical Journal, Feb. 10th, 1917, p. 207). He agrees that
"gunfire" per se has probably had little to do with the wetness of 1915 and 1916, but is not so sure
that" the vast quantity of dust thrown into the air by the myriad explosion of shells and bombs has
not had a causal relation to the extraordinary prevalence of cloud, and consequent abundant precipitation
during the past 2 or 3 years." He adds, "It is to be remembered, as proved experimentally by Mr.
John Aitkin, of Falkirk, that each particle of dust in the atmosphere acts as a condensor of aqueous
vapour."
It would be indeed, a strange result of the European War if it should be proved that dust due
to explosion of shells was in part responsible for the notable falling off in the admission of cases of scarlet
fever to Metropolitan Asylums Board hospitals. Whatever the cause may have been, the falling off
was very marked, and had the effect of obviating any difficulties that might have resulted from the
many other claims made on these hospitals during the last 2 years.